Different Types of Keys in DBMS
Keys in DBMS:
DBMS Keys are a data item that exclusively identifies a record. There are six different types of keys in DBMS:
Example: Account_number, Employee_number and customer_number uses as DBMS Keys because it specific identify a record store in a database.
Types of Keys in DBMS:
In DBMS, There are six types of keys are exists:
1. Super Key:
A Super key for an entity is a set of one or more attributes whose combined value uniquely identifies the entity in the entity set. Superset of any candidate key is also says Super key.
Example:
2. Primary Key:
The primary key uniquely identifies each record in a table and must never be the same for two records.
Example:
3. Candidate Key:
A candidate key is an attribute or a set of attributes that it identifies a record uniquely. These attributes or combinations of attributes say candidate keys.
Example:
Here, Two Candidate Keys are present in this table is given below:
4. Composite Key:
A composite key is a group of fields that it combines to uniquely identify a record. When we design a database, we will have tables that will use more than one column as a part of the primary key. So, it says a composite key or concatenated key.
Example:
Here Two Composite Keys are present in this table is given below:
5. Foreign Key:
In relation, the column whose data values correspond to the values of a key column in another relation says a Foreign Key.
Example:
Here, only one Foreign Key is present in both table is given below:
6. Secondary Key:
A secondary key is an attribute or combination of attributes that may not be a candidate key but classifies the entity set on a particular characteristic. A table can have multiple choices for a primary key but only one can be set as the primary key. All the keys are not the primary key that says Secondary Key.
Example:
In this table, Student_id, Roll_no, email_id are qualified to become a primary key. But since Student_id is only the primary key. Here Two Secondary Keys are present in this table is given below:
